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A nice 400cc scooter gets 65+ mpg and can easily do 70+ mph. If you want to do 100+ mph get the Burgman 650. It really is one of the best bikes I've ever owned and if I could only own one bike the Burg would be it.
For 10 to 12 miles round trip unless it's interstate anything pedal type or motorized will do. The biggest hurdle will be anything motorized will have a hard time in cooler weather getting up to ideal operating temp I that short of a distance.